1. Field of the Invention
The present invention relates to a method to discriminate a kind of an optical disc, and in particular, the present invention relates to a method to discriminate the kinds of the optical discs which have different thickness of a protecting layer to protect an information recording layer of the optical disc. Further, the present invention relates to an optical disc apparatus to which such optical disc discriminating method is applied.
2. Description of Related Art
Optical disc such as a compact disc (hereinafter referred to as a CD) and a digital versatile disc (hereinafter referred to as a DVD) are widely available from past. Further, optical disc which can record more large capacity of information, such as a Blu-ray disc (hereinafter referred to as a BD) and the like are developed recently for practical use. As a result, when reproducing or recording of the optical disc is performed by an optical disc apparatus, it is necessary to discriminate in advance what kind of the optical disc is loaded in the optical disc apparatus.
About a method to discriminate the kind of the optical disc, various kinds of technologies have been proposed heretofore. Among these technologies, there is a method to discriminate the kind of the optical disc based on difference of thickness of a protecting layer (it may also be referred to as a “transparent cover layer” or the like) which protects an information recording layer of the optical disc (See, JP-A-2007-095130, JP-A-2006-277848). When one example of them is shown, there is a method in which reflected light from surface of the optical disc and reflected light by the information recording layer are detected, difference of time interval between detection of the two reflected lights is measured, and the kind of the optical disc is judged based on it.
However, in the above described method which utilizes the difference of time interval between the detection of the reflection from the surface of the optical disc and the reflection by the information recording layer, a below described problem is caused. The detection of reflection from the surface of the optical disc or by the information recording layer is judged by result whether signal level of a prescribed signal which is obtained by processing of signal that is output from a photo detector, exceeds a prescribed threshold value, or not. However, there may be a case where chattering of signal happens when surface reflection or reflection by the information recording layer is detected, because of fluctuation of signal output from the photo detector, fluctuation of reflectance ratio of the optical disc, or the like. In such situation, there is a case where discrimination of the kind of the optical disc is not performed successfully.